I. We showed that the toxins alpha-sarcin, ricin, Shiga toxin and Shiga- -like toxin all inactivate protein synthesis in cells by attacking a highly conserved region near the 3'-end of 28S ribosomal RNA. All of these toxins were microinjected into Xenopus oocytes. Microinjection of deoxyoligonucleotides, ribonucleotides and ribozymes complementary to the same region of 28S RNA abolishes protein synthesis. II. During early development Xenopus replicates its DNA nearly as fast as E. coli in log phase; perhaps indicating that oocytes may be an -excellent source of DNA repair activity. We have investigated pyrimidine dimer repair by microinjecting UV-irradiated DNA into oocytes. Repair is demonstrated by the absence of pyrimidine dimers using UV-endonuclease and denaturing agarose gels. We have also studied DNA repair for alkylated and chemically modified DNA.